Transport in Plants

Describe water uptake by roots + role of root hair cells

-water uptaken by osmosis down conc gradient

-root hair cells have cytoplasm + vacuole with high cell contents to make wp more negative = drawing in water by osmosis

-root hair cells increase SA for absorption

Describe the apoplast, symplast and vacuolar pathway for water through the root

Symplast - cytoplasm to cytoplasm via plasmodesta

Apoplast - cell walls through fibres

Vacuolar - vacuole to vacuole

Describe how water moves into the root hair cells and then into the xylem

-water moves into root hair cells by apoplast pathway but forced into symplast pathway when it reaches endodermal cells as they are lined with suberin called a casparian strip

-strip is waterproof as suberin is hydrophobic

-water forced into symplast as ions are actively transported into endodermal cells to lower wp so water moves in my osmosis

-ions then actively transported into xylem to lower it's wp so water drawed in my osmosis into xylem

Describe structure + functions of xylem

-is a long continuous column made up of dead cells

-lined with lignin

-transports water and minerals

-provides mechanical strength + support

Describe the processes in involved in movement of water from roots to the leaves

Root pressure - due to mineral ions being actively transported from endodermal cells into the xylem = lowers wp so water moves in = creates hydrostatic (root) pressure which forces water up stem

Cohesion-tension - water flow is maintained by hydrogen bonds between water molecules and bonds between hydrophilic lignin and water to prevent backflow and help water move up the vessel - adhesion

Capillary action - movement of water up narrow tubes

Define Transpiration and Transpirational stream

-transpiration is the loss of water as water vapour by evaporation and diffusion out of open stomata leading to stream

-stream is the continual flow of water

Explain how temp affects transpiration rate

-higher temp = higher transpiration rate

-more kinetic energy in water molecules so evaporate out of stomata more

Explain how humidity affects transpiration rate

-lower humidity = higher transpiration rate

increases wp gradient between sub-stomatal air spaces and atmosphere

Explain how light affects transpiration rate

-more light = high rate

-as stomata tend to open in light so water vapour evaporates

Explain how wind speed affects transpiration rate?

high wind speed = higher transpiration rate

wind causes dispersal of water vapour around stomata = increases wp gradient

Explain adaptations of hydrophytes

little/no waxy cuticle as no need to conserve water

stomata only on upper surface as one side is submerged in water

poor xylem as water transport not needed

large air spaces for buoyancy

Explain adaptations of Xerophytes

adapted to live in dry conditions

rolled leaves to reduce SA for water loss

thick waxy cuticle

sunken stomata to increases humidity in pits to build up wp gradient to reduce water loss

hairs to trap water vapour to decrease wp gradient

Explain adaptations of Mesophyte

• close stomata at night to decrease water loss

• shed leaves in unfavourable conditions to reduce loss

• underground organs + dormant seeds survive winter